Ocean Timings and overlapping ?

[walters]

Why is there ocean waves? Why is there different timings for each wave how
does it do this?

How does the ocean water overlap? why is that?

[vinu]

This question is in human interest even centuries ago and put a
foundation for our basic understanding about the waves in the Ocean.

The main reason for , 'Why is there ocean waves', is the 'wind'. The
air over the ocean is under motion and it offers a stress over the
surface, which leads to surface undulations and waves. However the
spectrum is very broad and each have distinct physical characteristics.
In addition to the wind (of course it is major always), there are other
agencies which generate waves in a regular period. One example
is the Tide-generating forces (gravitational pull of the moon and other
planets), which undulate the ocean surface (pull outward) and
generate waves. For explaining the ocean waves that we usually
experience in our everyday life, for instance, the waves we see on the beach,
a wind generated mechanism will be suffice.

An Oscillation (generally) is a motion of an object bound to a particular field,
where a restoring force is acting. For example, a pendulum oscillates 'to
and fro', because the weight always tends the pendulum to be at its
equilibrium position. In the case of 'light waves', it is the
'electro-magnetic' field is the restoring medium. Likewise, the restoring
force in the Ocean wave is the gravity. Whenever the ocean surface is undulated
by wind (elevated or depressed), the gravity causes to restore it to the
equilibrium position, and this causes the surface to oscillate or the wave
births and as it is a fluid medium, the wave propagate through it.

Unlike the 'light waves', the 'ocean waves' have an interesting property.
In oceanography we call this property as 'Dispersion of the wave'. That is,
the 'light wave' has a 'constant speed' always through a given medium.
However in ocean waves, the speed is different for different waves.
Simply speaking, the wave speed depends on the wave number (number of waves
in unit length). In other words, the wave with larger wave length
travels faster than wave with smaller wave length. Thus, a set of waves generated at
a place travel with different speed, and this determine the
'Timing of each wave at any other place'. For a person on sea shore, the wave
impinging on the beach at every less than a minute, thus might
have generated somewhere in the open ocean by winds, and traveled all the way
to reach the coast. The longer waves reach first preceding by shorter
one later (may be in one or two days!). Oceanographers call this kind of
waves as 'swell'. Of course there could be waves generated with local
winds near the coast as well, and they are termed as 'sea'.

Like any other mechanical wave, ocean waves also interfere each other.
For instance, if a stretched wire is perturbating (disturbing) at two sides,
we can see waves generate from each of the perturbations and they interfere
in some manner. If we 'tune' the two disturbing forces, we can make
the situation that the wave does not travel along the string, but
the string oscillate up and down as a 'standing wave'. We can extend
the same situation to the ocean, where the surface is like a 'stretched
membrane' , and forcing by wind at various points. The interaction
might be a bit complicated in this case.

To read more interesting features about the ocean waves, the book
'Wind Waves' by Kinsman (1965), Prentice-Hall, Englewood Cliffs, NJ
is referred to as 'Classical'. There are also books, by
Proudman (1953) 'Dynamical Oceanography', Methuen, London.



Thanks
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